Apparatus for monitoring the presence of secretions in the respiratory system of a patient

ABSTRACT

An apparatus for monitoring the presence of secretions in an artificial respiratory system comprises at least one sensing element ( 20 ) to detect waves generated by said secretions and output a main signal ( 50 ), representative of at least one main parameter characteristic of the waves; a first processing block ( 30 ) connected downstream of said first sensing element ( 20 ), is set to input the main signal ( 50 ) and to generate a corresponding main output alarm signal ( 51 ), in the case in which the main parameter has a greater value than a predetermined threshold value.

The present invention relates to an apparatus for monitoring thepresence of secretions in the respiratory system of a patient.

More particularly, the apparatus in accordance with the presentinvention is adapted to be used for patients that are provided withrespiratory prostheses and/or are artificially ventilated followingknown ventilation modalities, or assisted in ventilation byoxygen-enriched devices for spontaneous ventilation.

It is known that artificially-ventilated patients (in particular thosepatients that are under intensive therapy) find it difficult toeliminate secretions from the respiratory tract.

It is therefore necessary that the medical assistance and/or nursingstaff should carry out removal of said secretions through a procedurecalled tracheobronchial aspiration. This procedure consists in insertinga pipe (aspiration tube) into the patient's respiratory tract and inaspirating the secretions therein present, thereby allowing the patientto carry out a correct ventilation.

It is very important for said procedure to be executed only if it isreally necessary; in fact, tracheobronchial aspiration also represents afactor of risk do to the occurrence of complications such as hypoxemia,atelectasis, cardiac arrhythmias, traumas of the respiratory tract,bronchial spasm, cough, increase in the intracranial pressure andinfections.

Consequently, the medical-nursing staff must pay attention so thatprocedures of tracheobronchial aspiration are not executed in theabsence of important secretion volumes.

On the other hand, it is not possible to neglect patients whoserespiratory tract is partly obstructed since the persistence of anexcessive amount of secretions at the respiratory tract can involvealterations in the patient's respiratory, cardiovascular and metabolicfunctions, that reveal themselves by reduction in the arterial oxygensaturation, increase in the respiratory frequency and the respiratoryfatigue, appearance of episodes of arterial hypertension, tachycardia,trouble with the acid-base balance, increase in the basal metabolism andstill other complications known to specialists.

In the light of the above, it is apparent that identifying the rightmoment for executing a tracheobronchial aspiration is very critical,taking into consideration the fact that serious complications can becaused either neglecting patients needing treatment, or executing theprocedure too often.

The known art provides devices capable of detecting and processingsignals relating to lung flows, volumes, pressures, in order to studypossible alterations in the lung mechanics and the respiratory workthrough construction of diagrams. The identification of the presence ofsecretions in said diagrams however, cannot be easily interpreted andinterpretation is not at all specific. Therefore such devices are notable to correctly and univocally associate the alterations of theflow-volume curve with the sure presence of stagnant secretions; inaddition said devices cannot be applied in combination with particularauxiliary ventilation apparatus and, above all, in the case of patientsthat are obliged to make exclusive use of an artificial respiratorytract.

Also known is use of apparatus utilising microphonic 5 transducers toformulate diagnoses relative to lung diseases, mainly as regardspneumology and/or lung physiopathology. For instance, magnitudesrelating to the respiratory cycle and spectral components of the lungsounds are employed to monitor and possibly classify lung diseases in apatient.

These microphones are occasionally applied to pre-established areas ofthe patient's body, such as the thorax for example, and generate signalsthat, once acquired, are submitted to an analog-digital conversion and asoftware processing through computerized stations and medicalvalidation. Generally therefore, a very complicated electronics isrequired for these devices and signals must be processed followingparticular algorithms 20 to be able to supply useful informationconcerning a patient.

At all events they are not able to communicate the presence of excessivesecretion volumes in the patient's respiratory track to the medicalassistance staff and consequently are not able to identify the correctmoment at which a tracheobronchial aspiration procedure is to beexecuted.

Therefore, it is an aim of the present invention to provide an apparatusfor monitoring the presence of secretions in the respiratory system of apatient that is artificially ventilated or is provided with respiratoryprothesis, which apparatus is able to signal to the nursing staff, themoment at which execution of a tracheobronchial aspiration is reallynecessary.

It is another aim of the present invention to provide an apparatus formonitoring the presence of secretions in a respiratory system which ischaracterized by a simple and cheap circuit structure.

It is a further aim of the present invention to provide an apparatus formonitoring the presence of secretions in a respiratory system, capableof detecting different magnitudes indicative of the presence ofsecretions, so as to compare said magnitudes with each other and carryout a very precise and reliable monitoring.

The foregoing and further aims are substantially achieved by anapparatus for monitoring the presence of secretions in the respiratorysystem of a patient that is provided with a respiratory prothesis or isartificially ventilated in accordance with the features described in theappended claims.

Further features and advantages will become more apparent from thedetailed description of a preferred but not limiting embodiment of anapparatus for monitoring the presence of secretions in the, respiratorysystem of a patient, shown in the accompanying drawings, in which:

FIG. 1 shows the apparatus of the present invention applied to theorotracheal cavity of an artificially-ventilated patient;

FIG. 2 shows a detail of FIG. 1, together with a block diagram of thecircuitry of the apparatus;

FIG. 3 is a block diagram of an auxiliary monitoring circuit of theapparatus.

The apparatus for monitoring the presence of secretions in anartificial-ventilation system in accordance with the present inventionis generally identified in the figures by reference numeral 1.

As can be viewed from FIGS. 1 and 2, apparatus 1 can be associated withan artificial-ventilation system, employed to enable patients with apulmonary insufficiency to correctly breathe. This system essentiallyconsists of a tubular duct 10 having a first portion 10 a insertable inthe patient's tracheal cavity, a second portion 10 b that is maintainedat the outside of the tracheal cavity, and a union element 10 cinterposed between the first and second portions 10 a, 10 b.

Through this structure, in combination with appropriate artificialventilation devices, a patent suffering from respiratory pathologies isallowed a correct respiration.

The apparatus in accordance with the present invention is employed formonitoring the presence of secretions in the patient's respiratorytract; practically, by means of the structure to be described in thefollowing, apparatus 1 is capable of monitoring when the accumulatedsecretions reach a predetermined volume and of communicating it to themedical and nursing staff.

Referring particularly to FIG. 2, apparatus 1 comprises a first sensingelement 20 that is mounted on the tubular duct 10.

The first sensing element 20 is arranged to detect waves generated bythe secretions accumulated in the ventilation system and to generate amain output signal 50, representative of at least one main parametercharacteristic of these waves. In other words, the main signal 50incorporates a main parameter, which is selected depending on theprocessing operations that are to be executed downstream, capable ofdescribing one or more of the physical features of the waves generatedby secretions.

These waves may for example comprise acoustic vibrations, propagatinginto the gasses present in the respiratory system and/or mechanicalvibrations, propagating through the patient's natural respiratory tractand the structure of the ventilation circuit, through a side wall 10 dof the tubular duct 10 for example.

For reception of vibrations of the acoustic type, the first sensingelement 20 comprises an appropriate sound detector 21, convenientlyembodied by a microphone of the electret type.

In order to limit noises from other sound or noise sources, the firstsensing element 20 can be positioned in a housing 11 defined in asound-proofing wall 12 of the tubular duct 10 associated, in the exampleherein shown, with the union element 10 c. Alternatively, the sounddetector 21 can be mounted on the second portion 10 b of the tubularduct 10, or at all events close to the second portion 10 b itself.

Alternatively, the first sensing element 20 can be set for detection ofmechanical vibrations, generated by secretions and propagating throughthe side wall 10 d of the duct. In this case, the first sensing element20 comprises an electromechanical transducer, preferably a piezoceramicbimorph transducer, at least partly in engagement by contact with thewall 10 d of the tubular duct 10, close to the union element 10 c, alongeither the first portion 10 a or the second portion 10 b. In this way,the mechanical vibrations generated by secretions can be detected by thefirst sensing element 20 that also generates the main signal 50incorporating information relating to said mechanical vibrations.

A first processing block 50 is positioned for connection downstream ofsaid first sensing element 20; it is set to input the main signal 50 andgenerate a corresponding main output alarm signal 51, should the mainparameter have a greater value than a predetermined threshold value.

The main parameter can be advantageously represented by the amplitude ofthe waves generated by secretions; thus, it is the amplitude of saidacoustic and/or mechanical vibrations to be monitored and processed.

In the case of acoustic vibrations, this means that, at the moment theintensity of the sounds generated by the secretions impinged on byrespiratory gas flows overcomes a predetermined threshold, the mainalarm signal 51 is generated, due to the fact that audio frequencies ofsome intensity can be only generated by the presence of secretionaccumulations of an important volume; consequently at said acousticvibrations the medical staff is informed about the necessity to carryout removal of the secretions accumulated within the respiratory tract.

On the other hand, in the case of mechanical vibrations, at the momentthe oscillation intensity of the secretions is greater than a givenlimit, the main alarm signal 51 is generated due to the fact thatsecretion accumulations generate particularly strong mechanicalvibrations; it is therefore apparent that if oscillations become strong,tracheobronchial aspiration is required, and the medical nursing staffis immediately warned. The information relating to the main parameter,as above mentioned, is transmitted by the main signal 50, generated bythe first sensing element 20.

In a preferred embodiment, it is the amplitude of the main signal 50that is used to represent the main parameter; in other words, theamplitude of the main signal 50 is a function of said main parameterand, consequently, of the amplitude of the waves generated bysecretions.

In particular, the main signal 50 is generated in such a manner that itsamplitude is proportional to the main parameter, i.e. to the amplitudeof the waves generated by secretions.

A choice of this type is particularly advantageous in order to make thestructure of the first processing block 30 as simple as possible, aspointed out in the following.

In fact, generally a comparison between the values taken by the mainparameter and the threshold value can be carried out by a circuitstructure comprising a memory, set to store said threshold value, and aCPU, capable of comparing the values incorporated in the main signal 50and the threshold value and generating, if required, the main alarmsignal 51.

If the amplitude of the main signal 50, as in the case of the presentinvention, is proportional to the amplitude of the waves generated bysecretions, it is possible to replace the above described circuitry witha filtering element 130 capable of amplitude-filtering the main signal50 and outputting the main alarm signal 51, should at least one of thespectral components defining the main signal 50 have a greater amplitudethan the threshold value.

In other words, this filtering element 130 is able to eliminate allspectral components of the main signal 50 of an amplitude less than thethreshold value, whereas the spectral components with an amplitudegreater than the threshold value are allowed to pass and are placed atthe entrance of the downstream-connected circuit blocks.

In particular, the filtering element 130 may comprise a diode 131,preferably an emitting diode of the LED type. In this case, the mainalarm signal 51 can be obtained through the light signal generated bythis emitting diode. Consequently, further circuit elements set togenerate the main alarm signal 51 are not required to be connected tothe filtering element 130.

In fact, the mere visual warning obtained by means of the LED can besufficient to inform the medical or nursing staff about the fact that atracheobronchial aspiration is necessary.

To make monitoring carried out by apparatus 1 more reliable, saidapparatus can have a combination of the two above described monitoringtechniques.

For the purpose, apparatus 1 may be provided with a second sensingelement 60 that is associated with the tubular duct 10 and performs thetask of detecting the waves generated by the secretions accumulatedwithin the respiratory system.

In particular, by way of example, the second sensing element 60 can bearranged for detection of the mechanical vibrations and operate incombination with the first sensing element 20 of the acoustic type.

In order to detect the mechanical vibrations from secretions, the secondsensing element 60 comprises an electromechanical transducer, preferablya piezoceramic bimorph sensor, at least partly positioned in contactwith the side wall 10 d of the tubular duct 10. The bimorph sensor canbe mounted either on the first portion 10 a of duct 10, or on the secondportion 10 b thereof, or also on the union element 10 c.

The second sensor 60 is capable of generating an auxiliary output signal70 incorporating at least one auxiliary parameter characteristic of saidwaves.

The second sensing element 60 is mounted at the union element 10 c ofthe tubular element 10 and is preferably housed within the union element10 c itself.

A second processing block 80 is positioned for connection downstream ofsaid second sensing element and is set to input the auxiliary signal 70and generate a corresponding auxiliary output alarm signal 71, shouldthe auxiliary parameter have a greater value than a predeterminedthreshold value.

Generally the auxiliary parameter represents a physical magnitudecharacteristic of the waves from secretions; advantageously, theauxiliary parameter may consist of the wave amplitude; thus, it will bethe amplitude of said mechanical vibrations to be monitored andprocessed by the circuitry connected downstream.

In the same manner as above described in relation to the main signal 50,the amplitude of the secondary signal 70 too can be a function of theauxiliary parameter. In particular, the amplitude of the auxiliarysignal 70 can be proportional to the auxiliary parameter.

By a signal structured in this way a direct link is created between theamplitude of the mechanical vibrations from the secretions and theamplitude of the auxiliary signal 70 generated by the second sensingelement 60.

Since the parameter to be evaluated is the amplitude of the auxiliarysignal 70, the second processing block 80 preferably comprises afiltering element 130 capable of amplitude-filtering the auxiliarysignal 70; in this manner the spectral components of the auxiliarysignal 70 having an amplitude less than the threshold value areeliminated, whereas those with a greater amplitude can be subsequentlyprocessed and help in creating the auxiliary alarm signal 71.

In order to make the circuit structure of the second processing block 80simple and cheap, said filtering element 130 may comprise a diode 131,preferably an emitting diode of the LED type; in this way, the auxiliaryalarm signal 71 is directly obtained through the light emission of theLED, so that the responsible staff can be visually warned about thenecessity of a tracheobronchial aspiration.

In the light of the above it is apparent that each of the two techniqueshitherto described can be also used individually; in other words,apparatus 1 can be provided with a single acoustic sensor or a singledetector of mechanical vibrations.

Alternatively, as above mentioned, in order to make signalling morereliable, apparatus 1 may comprise both a first sensor 20 of theacoustic type and a second sensor 60 for detection of mechanicalvibrations. In the last-mentioned case, apparatus 1 can be furtherprovided with a combination circuit 90, to receive the main alarm signal51 and auxiliary alarm signal 71 and generate a corresponding overallalarm signal 100, should said alarm signals 51, 71 be substantiallyreceived at the same instant. In this manner, the overall alarm signal100 is only generated when both the first and second processing blocks30, 80 signal the presence of an excessive volume of secretions withinthe respiratory tract; it is apparent that by combining the twomonitoring operations in this manner, there is a great increase in thereliability of the final signalling from apparatus 1.

The combination circuit 90 has a first input 90 a, associated with thefirst processing block 30, to receive the main alarm signal 51; in apreferred embodiment, a first photodetector 91 is positioned at thefirst input 90 a, so as to be optically coupled with the emitting diode131 of the first processing block 30. Upon reception of the main alarmsignal 51, the first photodetector 91 outputs a corresponding firsttransmission signal 101, destined to the downstream-connected circuitry.

The combination circuit 90 further has a second input 90 b associatedwith the second processing block 80, to receive the auxiliary alarmsignal 71; in a preferred embodiment, a second photodetector 92 ispositioned at the second input 90 b so as to be optically coupled withthe emitting diode 131 of the second processing block 80. Upon receptionof the auxiliary alarm signal 71, the second photodetector 92 outputs acorresponding second transmission signal 102.

The first and second transmission signals 101, 102 are received by alogic circuit 93, preferably embodied by a gate of the AND type, whichis set to generate said overall alarm signal 100, in the case of asubstantially simultaneous reception of said first and secondtransmission signals 101, 102.

Practically, the logic circuit 93 performs the task of recognizing themoment at which both the first and second detecting systems signal thepresence of excessive secretions in the respiratory tract and ultimatelygenerating the overall alarm signal destined to the nursing stuff.

This overall alarm signal 100 can be a signal either of the acoustic orof the visual type; according to an alternative embodiment, bothsignalling methods can be used simultaneously.

In order to make monitoring still safer and more reliable, apparatus 1can also use an IR (infrared) radiation detecting method carried out byan auxiliary monitoring circuit 110, diagrammatically shown in FIG. 3.The last-mentioned technique can be employed in combination with thefirst one (acoustic detection), the second one (detection of mechanicalvibrations) or both of them.

In this case, the emitting diode 131 of the first and/or secondprocessing block 30., 80 is an emitter of IR radiation 140 at apredetermined wavelength, preferably of about 4.2 m.

The first and/or second processing block 30, 80 therefore, instead ofgenerating (main and/or secondary) visible alarm signals, when anexcessive volume of secretions is detected, emit an IR radiation 140passing through the respiratory gases present within the tubular duct10.

The auxiliary monitoring circuit 110 is provided with a detectingelement 111, preferably a photodiode 113 which is coupled with theemitting diode 131 for reception of the IR radiation 140 passed throughthe gases present in the tubular duct 10.

A signalling circuit 112, connected downstream of the detecting element111, outputs a warning signal 120 if a reduction in the intensity of thereceived IR radiation 140 is detected.

In fact, in the presence of volumes of secretions there is a greatincrease in the concentration of carbon dioxide within the respiratorygases, since secretions give off amounts of CO₂. This gives rise to agreater absorption of the IR radiation 140 by the CO₂ therein presentand, as a result, the intensity of the radiation received by thedetecting element 111 is smaller if there is a high concentration of CO₂in the respiratory gases and, consequently, if the volume of theaccumulated secretions is of such an amount that a tracheobronchialaspiration is made necessary.

It is apparent that the auxiliary monitoring circuit 110 can beadvantageously associated with both the first processing block 30 andthe second processing block 80, by associating the detecting element 111with the logic circuit 93 of the combination circuit 90.

In fact, an IR radiation-emitting diode can be connected downstream ofsaid logic circuit 93 so that the radiation passes through therespiratory gases and is at least partly absorbed by the carbon dioxidepresent in these gases. Therefore the detecting element 111 is suchpositioned that it picks up said infrared radiation and enables thesignalling circuit 112 to generate the warning signal 120, should theintensity of the received IR radiation decrease to a great extent.

The invention achieves important advantages.

First of all, the apparatus in accordance with the present inventionenables the presence of secretions within the patient's respiratorytract to be monitored with great reliability.

In particular, by virtue of the use of one or more of the abovedescribed,detection techniques it is possible to avoid the patient beingsubmitted to bronchial aspiration procedures when it is not necessaryand, on the other hand, the responsible staff can be timely warned whenthis procedure is to be really executed.

In addition, the circuit elements herein employed are simple and cheap,since the generated signals are not digitized and therefore nomicroprocessor is required to be used.

A further advantage is found in the fact that, should visiblelight-emitting diodes be utilised in the first and/or second processingblock, the amplitude of the main signal and/or the auxiliary signal ismonitored and the corresponding alarm signal is generated by means of asingle circuit element, so that the manufacturing costs and the hardwarecomplexity of the apparatus are minimized.

1-21. (cancelled)
 22. An apparatus for monitoring the presence ofsecretions in the respiratory system of a patient provided with arespiratory prothesis, having at least one tubular duct consisting of afirst portion at least partly insertable in the patient's orotrachealcavity and of a second portion to be positioned externally of thetracheal cavity, further comprising: at least one sensing element to beassociated with the tubular duct to detect waves generated by saidsecretions and output a main signal, representative of at least one mainparameter characteristic of said waves, said main signal being definedby one or more spectral components, each having a respective amplitude;a first processing block, connected downstream of said first sensingelement and set to input said main signal and generate a correspondingmain output alarm signal, when said main parameter has a value greaterthan a predetermined threshold value.
 23. An apparatus as claimed inclaim 22, wherein said first sensing element comprises an acousticdetector, capable of detecting said waves, which waves comprise acousticvibrations generated by said secretions and propagating through thegases present in said duct.
 24. An apparatus as claimed in claim 23,wherein said acoustic detector is a microphone of the electret type. 25.An apparatus as claimed in claim 22, wherein said first sensing elementis positioned in a housing defined in a sound-proofing wall of thetubular duct.
 26. An apparatus as claimed in claim 22, furthercomprising: a second sensing element to be associated with said tubularduct to detect the waves generated by said secretions and output anauxiliary signal, representative of at least one auxiliary parametercharacteristic of said waves, said auxiliary signal being defined by oneor more spectral components, each having a respective amplitude; asecond processing block, connected downstream of said second sensingelement and set to input said auxiliary signal and generate acorresponding auxiliary output alarm signal,when said auxiliaryparameter has a greater value than a predetermined threshold value. 27.An apparatus as claimed in claim 22, wherein the first sensing elementcomprises an electromechanical transducer capable of detecting saidwaves, which waves comprise mechanical vibrations generated by saidsecretions and propagating through at least one side wall of the tubularduct.
 28. An apparatus as claimed in claim 27, wherein saidelectromechanical transducer is a piezoceramic bimorph sensor positionedat least partly in contact with said side wall.
 29. An apparatus asclaimed in claim 22, wherein said main parameter consists of theamplitude of said waves.
 30. An apparatus as claimed in claim 29,wherein the amplitude of said main signal is a function of said mainparameter.
 31. An apparatus as claimed in claim 30, wherein theamplitude of said main signal is proportional to said main parameter.32. An apparatus as claimed in claim 22, wherein said first processingblock comprises a filtering element capable of amplitude-filtering saidmain signal and generating the main output alarm signal when at leastone of the spectral components of the main signal has a greateramplitude than said threshold value.
 33. An apparatus as claimed inclaim 32, wherein said filtering element comprises a diode.
 34. Anapparatus as claimed in claim 33, wherein said diode is a LED typeemitting diode, said main alarm signal being obtained by a light signalgenerated by said emitting diode.
 35. An apparatus as claimed in claim22, wherein said tubular duct further comprises a union elementinterposed between said first and second portions.
 36. An apparatus asclaimed in claim 22, wherein said first sensing element is positionedclose to the second portion of the duct.
 37. An apparatus as claimed inclaim 26, wherein said tubular duct further comprises a union elementinterposed between said first and second portions, said second sensingelement being mounted close to the union element of said duct.
 38. Anapparatus as claimed in claim 26, further comprising a combinationcircuit having a first input associated with said first processingblock, and a second input associated with said second processing block,said combination circuit being set to receive said main and auxiliaryalarm signals and to generate a corresponding overall alarm signal whena substantially simultaneous reception of said main and auxiliary alarmsignals takes place.
 39. An apparatus as claimed in claim 38, whereineach of said first and second processing block comprises a LED typeemitting diode, each of said main alarm signal and auxiliary alarmsignal being obtained by a light signal generated by said emittingdiode, said combination circuit comprising: a first photodetector,positioned at said first input and optically coupled with the emittingdiode of the first processing block, said first photodetector beingcapable of picking up an emission of the main alarm signal andoutputting a corresponding first transmission signal; a secondphotodetector, positioned at said second input and optically coupledwith the emitting diode of the second processing block, said secondphotodetector being capable of picking up an emission of the auxiliaryalarm signal and outputting a corresponding second transmission signal;a logic circuit, preferably of the AND gate type, set to input saidfirst and second transmission signals and to generate said overall alarmsignal, when a substantially simultaneous reception of said first andsecond transmission signals takes place.
 40. An apparatus as claimed inclaim 39, wherein said overall alarm signal is a signal of the opticaland/or acoustic type.
 41. An apparatus as claimed in claim 32, whereinsaid filtering element comprises an infrared radiation emitter, saidapparatus further comprising at least an auxiliary monitoring circuitprovided with: a detecting element coupled with the emitting diode andset to receive the infrared radiation from said emitting diode; asignalling circuit connected downstream of said detecting element andcapable of outputting a warning signal on the occurrence of a reductionin the intensity of the infrared radiation received.
 42. An apparatus asclaimed in claim 41, wherein said detecting element is a photodiodecoupled with said emitting diode.
 43. An apparatus as claimed in claim22, wherein the at least one sensing element is mounted on the tubularduct.
 44. An apparatus as claimed in claim 26, wherein the secondsensing element comprises an electromechanical transducer capable ofdetecting said waves, which waves comprise mechanical vibrationsgenerated by said secretions and propagating through at least one sidewall of the tubular duct.
 45. An apparatus as claimed in claim 44,wherein said electromechanical transducer is a piezoceramic bimorphsensor positioned at least partly in contact with said side wall.
 46. Anapparatus as claimed in claim 26, characterized in that said auxiliaryparameter consists of the amplitude of said waves.
 47. An apparatus asclaimed in claim 46, wherein the amplitude of said auxiliary signal is afunction of said main parameter.
 48. An apparatus as claimed in claim46, wherein the amplitude of said auxiliary signal is proportional tosaid auxiliary parameter.
 49. An apparatus as claimed in claim 26,wherein said second processing block comprises a filtering elementcapable of amplitude-filtering said auxiliary signal and generating theauxiliary output alarm signal in the case in which at least one of thespectral components of the auxiliary signal has a greater amplitude thansaid threshold value.
 50. An apparatus as claimed in claim 49, whereinsaid filtering element comprises a diode.
 51. An apparatus as claimed inclaim 50, wherein said diode is a LED type emitting diode, saidauxiliary alarm signal being obtained by a light signal generated bysaid emitting diode.
 52. An apparatus as claimed in claim 35, whereinsaid first sensing element is positioned on said union element.
 53. Anapparatus as claimed in claim 37, wherein said second sensing element ishoused within said union element.
 54. An apparatus as claimed in claim49, wherein said filtering element comprises an infrared radiationemitter, said apparatus further comprising at, least an auxiliarymonitoring circuit provided with: a detecting element coupled with theemitting diode and set to receive the infrared radiation from saidemitting diode; a signalling circuit connected downstream of saiddetecting element and capable of outputting a warning signal on theoccurrence of a reduction in the intensity of the infrared radiationreceived.
 55. An apparatus as claimed in claim 54, wherein saiddetecting element is a photodiode coupled with said emitting diode.